1. Field of the Invention
The present invention relates to a substrate processing apparatus and a reaction container, more particularly, to a substrate processing apparatus and a reaction container used in one step of producing process of a semiconductor device for processing a substrate in a reaction chamber, and more particularly, to an improvement of a gas introducing portion which supplies gas to a substrate.
2. Description of the Related Art
A conventional technique for processing a substrate in a reaction chamber by a CVD (Chemical Vapor Deposition) method or an ALD (Atomic Layer Deposition) method will be briefly explained with reference to FIG. 14 while taking a vertical type substrate processing apparatus as an example.
FIG. 14 is a schematic sectional view of the inside of a reaction tube which is a reaction chamber in the conventional vertical type substrate processing apparatus.
A plurality of wafers 107 are stacked on a boat 108 as substrates to be processed. The boat 108 is inserted into a reaction tube 106. A gas nozzle 101 as a gas introducing portion for processing the wafers 107 in the reaction tube 106 is provided in the reaction tube 106.
The gas nozzle 101 is provided with a plurality of gas nozzle holes 103 (five in the example shown in FIG. 14). With this arrangement, processing gas flows into the gas nozzle 101 from a gas introducing opening 105, and is supplied to the wafers 107 from the gas nozzle holes 103.
The gas supplied to each wafer 107 passes through a process for forming a desired film on the wafer 107 and then, is discharged out from the reaction tube 106 through an exhaust opening 118.
However, when all of the gas nozzle holes 103 provided in the gas nozzle 101 have the same opening areas, there is a problem that a flow rate and flow velocity of gas supplied from the gas nozzle holes 103 to the wafers 107 are reduced from an upstream side closer to the gas introducing opening 105 toward a downstream side further from the opening 105.
That is, if the apparatus for collectively processing the plurality of wafers 107 shown in FIG. 14 is considered from a viewpoint of gas supply with respect to each of the wafers, it seems that the gas nozzle 101 supplies gas uniformly to the wafers 107, but in reality, a difference in the gas flow rate or flow velocity is generated, and the gas is not supplied to all of the wafers 107 under the same conditions.
For example, if the five gas nozzle holes 103 provided in the gas nozzle 101 are defines as a first hole, a second hole, . . . and a fifth hole from the upstream side closer to the gas introducing opening 105 of the gas nozzle 101 toward the downstream further from the opening 105, and if the flow rates of gas supplied from the respective gas nozzle holes 103 are defined as q1, q2 . . . q5, a relation of q1>q2> . . . >q5 is established.
Concerning the flow velocities of gas also, a velocity of gas from the first gas nozzle holes 103 is the fastest, and velocities of gas from the second, third, . . . are gradually reduced.
As a result, the flow rates and flow velocities of gas supplied to the wafers 107 become nonuniform.
Therefore, in the process of wafers which largely depends of a supply amount of gas, the film forming states of the stacked wafers 107 become nonuniform.
Referring back to FIG. 14, a cause of the nonuniformity of the supply amount of gas will be considered.
In the gas nozzle 101 in a state in which gas is supplied to the wafers 107, a gas flow rate between the introducing opening 105 and the first gas nozzle hole 103 is defined as q00 and a gas pressure therebetween is defined as p0. Next, a gas flow rate between the first and second gas nozzle holes 103 is defined as q01 and a gas pressure therebetween is defined as p1. Similarly, a gas flow rate between the n−1-th and n-th gas nozzle holes 103 is defined as q0(n−1) and a gas pressure therebetween is defined as pn−1.
A flow rate of gas injecting from the n-th gas nozzle hole 103 is defined as qn.
At that time, gas flow rates qn (n=1, 2, . . . ) injecting from the plurality of gas nozzle holes 103 provided from the upstream side to the downstream side and having the same opening areas are reduced from the upstream gas nozzle hole toward the downstream gas nozzle hole as shown in the following expression (1):q1>q2> . . . >qn−1>qn  (1).
This is because, in the case of gas flowing from the upstream side toward the downstream side through the gas nozzle 101, its gas flow rate q0(n−1) is reduced by a gas flow rate qn injecting from the gas nozzle hole 103 when the gas passes through the gas nozzle hole 103, and the gas flows toward a next gas nozzle hole. A flow rate of gas after the gas passed through the gas nozzle hole 103 is reduced from the upstream side toward the downstream side as shown in the following expression (2):q0n=q0(n−1)−qn  (2)
At that time, a gas concentration of fluid in the gas nozzle 101 is reduced by a flow rate of gas injecting from the gas holes from the upstream side toward the downstream side. Since there is a correlation between the gas concentration and gas pressure, a gas pressure pn at a location in the gas nozzle 101 corresponding to the gas nozzle hole 103 is reduced from the upstream side toward the downstream side as shown in the following expression (3):p1>p2> . . . >pn−1>pn  (3)
Therefore, flow rates of gas injecting from the respective gas nozzle holes 103 do not become equal to each other. If an opening area of the gas nozzle hole 103 is defined as S, a flow velocity V of gas injecting from the gas nozzle hole is expressed as shown in the following expression (4):V=qn/S  (4)
Since the flow rates of gas injected from the respective gas nozzle holes 103 are not equal to each other, if the opening areas of the nozzle holes are the same, flow velocities of gas injected from the respective gas nozzle holes 103 become different. In the above-described conventional gas nozzle 101, since the flow rates and flow velocities of gas injected from the respective gas nozzle holes 103 are different, it is considered that gas cannot be supplied to the wafers uniformly.
To solve the above problem, two conventional solutions have been proposed.
According to a first solution, opening areas of the gas nozzle hole 103 are increased from the upstream side toward the downstream side, and a gas flow rate which is reduced toward the downstream side is supplemented by increasing the opening area. However, if the gas flow rates are equalized by adjusting the opening areas, the gas flow velocities are adversely varied depending upon the size of the opening area. Therefore, gas injecting from the gas nozzle holes 103 is nonuniform in the flow velocity.
According to a second solution, a capacity of the gas nozzle itself is increased to such a degree that such a large amount of gas that the injecting amount can be ignored is stored so that even if gas is injected from the gas nozzle holes 103 from the upstream side toward the downstream side, gas pressures in the gas nozzle 101 at locations corresponding to the respective gas nozzle holes 103 are not changed, thereby equalizing the flow rates of gas injecting from the gas nozzle holes 103. However, if the capacity of the gas nozzle itself is increased to such a size that the gas pressure in the gas nozzle 101 is not affected by the gas injecting amount, since there is limitation in space of the reaction chamber which accommodates the gas nozzle, this is not practical.
The above problem is not limited to a wafer, and a substrate in general also has the same problem.